Late Bee?

by Carl Strang

On May 20 at Mayslake Forest Preserve I saw this queen Bombus impatiens bumblebee digging in a small area in the south savanna.

There had been many days of warm weather, and so I would have thought by that point all the queens would have found nest sites and begun their first broods. Already I was seeing worker Bombus bimaculatus in my garden at home. So, what was the digging queen’s story? I don’t know any other reason why a queen would dig. If she sensed a cavity in the soil below that spot, a little digging might get her a nest hole. It seemed late to be searching still. Perhaps she had a nest, lost it, and had to start over.

On the other hand, given her species it’s not a total disaster. Bombus impatiens is the one species whose activity spanned the entire season at Mayslake last year. I saw them as late as October 5. The latest other bumblebee was a B. griseocollis on August 25. I haven’t been studying bumblebees long enough to know whether this is typical, but in any case it seems there still is plenty of time for this impatiens queen to get going.

Bumblebee Dynamics

by Carl Strang

In my last update on bumblebees  at Mayslake Forest Preserve I described the 5 species I had observed to that point. In the subsequent few weeks there have been a couple of changes to report. First is the apparent addition of a 6th species.

Bombus pennsylvanicus 1b

I believe this to be Bombus pennsylvanicus. At first glance it is very close to Bombus auricomus, which I described earlier. Both are relatively large bumblebees, both have lots of black on the thorax (especially on the sides), and both have segments 2 and 3 of the abdomen all yellow. However, auricomus has a cleaner, sharper look. All the yellow areas are bright, pure yellow. The black areas are unblemished by hairs of other colors. Both black and yellow areas are sharply defined, and correspond to the edges of body segments. If I am correct in my identification, pennsylvanicus has a muddier look. The yellow of the dorsal abdomen spills a little onto the first segment as you can just see in the above photo. Also, the yellow area of the posterior dorsal thorax has some black hairs mixed in, and the black on the sides of the thorax has some yellow hairs mixed in.

The more astonishing change is the nearly total disappearance of Bombus bimaculatus over the past three weeks. Through July, this was the most common bumblebee at Mayslake, with numbers exceeding those of all other species combined. I was away a week for Roger Raccoon Club , and returned to find the bimaculatus nearly gone. Now I see at most one or two a day. The other common small species, Bombus impatiens, continues essentially unchanged.

Bombus impatiens worker b

This is my first year of following the bumblebees at Mayslake. I don’t know if this disappearance is usual, and I don’t know what it means. I doubt that the species has a limited season, as bumblebees generally continue through the summer. Some of the native, solitary bees are specific to a single flower species and thus have defined seasons, but bumblebees are generalists. They are known to monitor changes in flower abundance and to travel miles, and so may have abandoned Mayslake for an abundant appearance of other flowers elsewhere. Disease might have impacted one colony, but for all the local colonies to be affected with no obvious change in other species seems unlikely (though the uncommon Bombus griseocollis also has been absent in August).

One day earlier this week I saw a couple odd looking bumblebees that seemed clumsy on the flowers.

Bombus bimaculatus or griseocollis male b

Their markings were like those of griseocollis or bimaculatus, not precisely fitting either. They had enormous eyes, and were larger than most workers of either species. Photos showed them also to have unusually long antennae. These are males. What, if anything, their sudden appearance has to do with the absence of their species’ workers is another piece of the puzzle that needs fitting.

If you build it…

by Carl Strang

Our yards are habitats for wildlife. We have no choice in that. We can, however, influence what kinds of wildlife will visit us or live with us on the land. This is true even for a tiny yard like mine. Here are some examples from my prairie flowerbeds, which are approaching their peak now.

Prairie garden 26JL09 b

I have planted royal catchflies all out of proportion to their presence in our local prairies.

Royal catchfly b

As a result, I can count on regular visits from ruby-throated hummingbirds in July and August. Here is this year’s happy camper, photographed through the kitchen window.

Yard hummer 1b

I kind of like this impressionistic view of the same bird.

Yard hummer 2b

Red tubular flowers shout “hummingbird” to ecologists, and to the birds themselves. I wonder if royal catchfly flowers also have evolved the means to defeat nectar thieves.

Bombus bimaculatus yard b

This Bombus bimaculatus bumblebee behaved as though it were in one of those sticky-slow-motion nightmares. The hairs on the royal catchfly calyx either were affecting it chemically, or physically had grabbed it. It wasn’t struggling strongly, so I suspect the former. As far as I know, no bumblebee has a tongue long enough to reach the nectaries of this flower from the front. Bumblebees are known to pierce such flowers from the outside, getting nectar but bypassing the anthers, therefore not serving the plant’s need for cross pollination. Such nectar thievery could provide selective pressure favoring any adaptation in the plant that might prevent the would-be perps from being successful.

In any case, I have plenty of bimaculatus visiting my other flowers, and also a few Bombus griseocollis.

Bombus griseocollis yard b

A final species for this time is the monarch.

Monarch larva b

This half-grown caterpillar is doing well on one of my butterfly weed plants.

Progress on Bumblebees

by Carl Strang

Earlier I posted some background on bumblebees . I find that I made an error or two there, I since have found additional species at Mayslake Forest Preserve, and also some added web sites specific to Illinois bumblebees that have helped immensely. The total list for Mayslake at this point includes 5 species, and I showed a photo from Fullersburg Woods of a 6th, Bombus vagans, in that earlier post. There are 9 species total for Illinois, of which 2 are rare. (Here I am not counting the nest-parasite “cuckoo bumblebees,” of which there are 2, but which I have not yet encountered). To this point in the season, the most common species has been Bombus bimaculatus, both at Mayslake and in my garden at home. It has a yellow thorax except for a black dot on top, the first (basal) abdominal segment is yellow, the second segment is yellow in the center front edge but black on the ends and back edge. Otherwise the abdomen is black.

Bombus bimaculatus 2b

The patch of yellow on the second segment often is small and hidden by the wings, so care is needed to distinguish bimaculatus from another common species (though perhaps less common locally than I implied in that earlier post), Bombus impatiens. The main difference from bimaculatus is that the yellow on impatiens’ abdomen is confined to the first segment.

Bombus impatiens queen 2b

One correction I need to make to that earlier post is that the dead bumblebee I featured was not Bombus fervidus after all. That bee had a black basal abdominal segment, where in fervidus the first 4 segments all are yellow. I have found a few live members of the dead bee’s species at Mayslake.

Bombus auricomus 10b

This is Bombus auricomus, which is regarded as “uncommon” in Illinois. Here, the first segment is entirely black, segments 2 and 3 entirely yellow. The sides of the thorax are black, and as the next photo shows, there is a large black area in the center of the dorsal (top) thorax.

Bombus auricomus 2b

At Mayslake I have seen only a few of these, always in the same place, so I believe there is only one colony of them on the preserve. Compared to other bumblebees they are large and very active. Bombus fervidus is at Mayslake, too.

Bombus fervidus 3b

Here you can see that the basal segment also is yellow, as is the entire thorax except for a black band across the back between the wings. In that earlier post I mentioned the ecological significance of differences in tongue lengths among species. Get a load of the tongue length on that fervidus!

Bombus fervidus tongue b

The 5th Mayslake species to date is Bombus griseocollis.

Bombus griseocollis swamp milkweed 3b

In this one the forward edge of the second abdominal segment is orange, but the back edge is black. The color on the second segment extends closer to the edge than it did in bimaculatus.

Bombus vagans, which I have seen at Fullersburg but not yet at Mayslake, has the first two abdominal segments yellow all the way to the back edge.

Bombus vagans 1b

That leaves only one species of bumblebee which is said to be common in Illinois but which I have not yet observed: Bombus pensylvanicus (listed in some references as B. americanorum). That one is most similar to B. auricomus, but typically has the top rear part of the thorax black or orange, and the first abdominal segment has some yellow on its rear edge.

Here are some web references. For a really nice diagrammatic comparison of these color patterns you can download a pdf file called “Bumble Bees of Illinois and Missouri”. A site with additional identification and ecological information is the beespotter site.

%d bloggers like this: